Molluscum contagiosum (MC) is a common skin infection caused by molluscum contagiosum virus (MoCV), a dermatotropic poxvirus. MC presents as single to multiple skin lesions that last from months to years. Transmission is by direct skin-to-skin contact or by indirect contact with fomites. MC lesions are solely restricted t human skin and occur in children, adults, and immunosuppressed individuals. While the lesions are benign, they are often unsightly and thus are psychologically distressful to patients and parents. MC occurs in 2-10% of the worldwide population. In the USA, it constitutes about 1% of all diagnosed skin disorders and occurs in almost 5% of children. In immune-compromised individuals, MC is severe and protracted. Between 5- 18% of HIV patients have MC. Despite the huge burden of disease and the associated significant healthcare costs, there are no extramural NIH-funded projects that specifically study this virus. The major impediment in researching MoCV and finding potential therapeutic cures for MC has been the inability of MoCV to propagate in any type of cultured cells. The objective of this R21 project is to use various novel strategies to identify a system that would allow replication of MoCV in cell culture. We hypothesize that the inability to propagate MoCV in cells in culture is linked to the inability of MoCV to downregulate a cell's innate anti-viral responses. It also reflects unique properties of the human epidermis in vivo that are not reproduced during culture in vitro. We hypothesize that this block in productive infection can be overcome by manipulation of cells in culture to create an intracellular environment that would allow the full MoCV life cycle to be carried out. By establishing models for the growth of MoCV in cell culture and identifying the factors that regulate its replication in keratinocytes, we will gain insights into unique features of skin cells that allow dermatotropic viruses like MoCV to grow and spread in the skin, which will, in the future, serve as a basis for further study and potential development of therapeutics. To test these concepts we will: * Determine at what stage MoCV infection is blocked in both primary human keratinocytes and immortalized cells * Manipulate the host cell microenvironment with poxviral proteins not expressed by MoCV * Manipulate the host cell innate-antiviral responses by targeting cellular proteins By combining Penn's on-campus research expertise in poxvirology and human epidermal biology, we believe that we are poised to make a major advance in poxvirology and discover a way to allow the propagation and spread of MoCV in cell culture systems. Support through this R21 application will allow us begin the steps to reach this important and significant goal.